1. Field of the Invention
The invention relates to a piston for an internal combustion engine, having an upper part, the upper side of which forms the piston crown, and a lower part. The upper part has a circumferential collar formed onto the piston crown radially on the outside, facing downward in a direction facing away from the piston crown. A compression ring groove is disposed on a radial outside of the collar, having a circumferential ring rib disposed on the underside of the upper part, radially within the collar. The axial length of the collar is less than the distance from the lower face surface of the ring rib to the piston crown. The lower part has a circumferential wall radially on the outside, facing upward, in the radial outside of which wall ring grooves are formed. The upper face surface of the lower part has the same radial distance from the piston axis as the lower face surface of the collar. There is a circumferential contact part formed onto the lower part, facing upward and disposed radially within the wall. The upper face surface of the circumferential contact part has the same distance from the piston axis as the lower face surface of the ring rib. The upper face surface of the circumferential contact part has an axial distance from the plane defined by the face surface of the wall, which distance corresponds to the difference between the distance from the lower face surface of the ring rib to the piston crown and the length of the collar, so that when the upper part is connected with the lower part by the friction-welding, the face surfaces of the ring rib, the collar, the wall, and the contact part form friction-welding surfaces. A closed ring-shaped cooling channel delimited radially on the outside by the collar and by the wall and radially on the inside by the ring rib and by the contact part is obtained in this manner. The region between the contact part is formed by a crosspiece having an opening that lies in the center, which crosspiece forms the lower delimitation of a central cooling cavity. The cooling cavity is delimited at the top by the piston crown and radially on the outside by the contact part and by the ring rib. Two skirt elements that lie opposite one another are disposed on the underside of the lower part, which elements are connected with, one another by means of two pin bosses that lie opposite one another, each having a pin bore.
2. The Prior Art
A piston of the type stated initially is described in International Application Publication No. WO 02/33291. This piston has an oil channel disposed close to the bottom of the cooling cavity and of the cooling channel, which oil channel connects the cooling cavity with the cooling channel. This prevents the formation of an oil accumulation, particularly in the cooling cavity, and thus worsens the cooling of the piston crown, which is subject to great thermal stress, because the oil situated in the cooling cavity can flow back into the cooling channel by way of the oil channel, and oil flows from the cooling channel into the cooling cavity only if the oil level of the oil situated in the cooling channel is higher than the level of the oil situated in the cooling cavity. In this way, the through-flow of oil from the cooling channel by way of the cooling cavity to the oil drain opening is furthermore hindered, reducing the continued flow of cooling oil, and thus leading to further deterioration of the cooling of the piston crown.